Optical test apparatus and optical test method

ABSTRACT

According to one embodiment, an optical test apparatus includes a light convergence element, an optical filter, and an image sensor. The light convergence element converges light from a subject. The optical filter is arranged on an optical axis of the light convergence element. The image sensor is arranged in an effective region not crossing the optical axis of the light convergence element, and receives light passing through the light convergence element and the optical filter.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2018-211685, filed Nov. 9, 2018, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an optical testapparatus and an optical test method.

BACKGROUND

In various industries, contactless test techniques have becomeimportant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of a configuration of anoptical test system according to the embodiment.

FIG. 2 is a bird's eye view schematically showing a configurationexample of an optical device of FIG. 1.

FIG. 3 is an x-z sectional view showing an example of the configurationof the optical device of FIG. 1.

FIG. 4A is a schematic view showing an example of an x-y cross sectionof an aperture of a first optical filter of FIGS. 2 and 3.

FIG. 4B is a schematic view showing an example of an x-y cross sectionof an aperture of a second optical filter of FIGS. 2 and 3.

FIG. 5A is a schematic view of an x-z cross section for explaining aneffective region for the optical device of FIG. 1.

FIG. 5B is a schematic view of an x-y cross section for explaining theeffective region for the optical device of FIG. 1.

FIG. 6 is a schematic view for explaining an example of a ray path inthe optical device of FIG. 1.

FIG. 7 is a flowchart showing an example of calculation processingperformed by the optical test apparatus of FIG. 1.

FIG. 8 is a diagram for explaining the relationship between a distancebetween an optical axis and an imaging axis in the optical device ofFIG. 1, and detection sensitivity for a three-dimensional position of anobject point.

FIG. 9 is a diagram for explaining an unmeasurable region in the opticaldevice of FIG. 1.

FIG. 10 is a diagram for explaining a measurable region in the opticaldevice of FIG. 1.

FIG. 11 is an x-z cross-sectional view showing an example of aconfiguration of an optical device according to a first modification.

FIG. 12A is a schematic view showing an example of an x-y cross sectionof an aperture of a third optical filter according to a secondmodification.

FIG. 12B is a schematic view showing an example of an x-y cross sectionof an aperture of a fourth optical filter according to the secondmodification.

FIG. 13 is a schematic view of an x-y cross section for explaining anexample of an arrangement of imaging planes in a case where the opticaldevice of FIG. 1 has a plurality of image sensors.

DETAILED DESCRIPTION

According to one embodiment, an optical test apparatus includes a lightconvergence element, an optical filter, and an image sensor. The lightconvergence element converges light from a subject. The optical filteris arranged on an optical axis of the light convergence element. Theimage sensor is arranged in an effective region not crossing the opticalaxis of the light convergence element, and receives light passingthrough the light convergence element and the optical filter.

Various Embodiments will be described hereinafter with reference to theaccompanying drawings. Each drawing is schematic or conceptual and therelationship between the thickness and the width of each part and thesize ratio between the respective parts are not necessarily the same asactual ones. In addition, even when the same portions are shown, theportions are sometimes shown in different dimensions and ratiosdepending on the drawings. Note that in this specification and therespective drawings, the same reference numerals denote the samecomponents described with reference to the drawings already referred to.A detailed description of such components will be omitted asappropriate.

Light or a light ray in a description of each embodiment is not limitedto visible light or a visible light ray. However, the followingdescription will exemplify a case in which white light is used asenvironment light. The light ray may also be a light beam.

First, the configuration of an optical test system 1 according to thepresent embodiment will be described in detail with reference to thedrawings.

FIG. 1 is a block diagram showing an example of the configuration of theoptical test system 1 according to the present embodiment. As shown inFIG. 1, the optical test system 1 includes an optical test apparatus 10and a display 90. The optical test apparatus 10 includes an opticaldevice 20, processing circuitry 70, and a memory 80.

FIG. 2 is a bird's eye view schematically showing a configurationexample of the optical device 20 of FIG. 1. FIG. 3 is an x-zcross-sectional view showing an example of the configuration of theoptical device 20 of FIG. 1. As shown in FIGS. 1, 2, and 3, the opticaldevice 20 includes an optical system 30 and an image sensor 60. As shownin FIGS. 2 and 3, the optical system 30 includes a lens 31, a firstoptical filter 33, and a second optical filter 35.

In the present embodiment, each of x-axis, y-axis, and z-axis is definedas follows. The z-axis serves as the optical axis OA of the lens 31. The+z direction is a direction from the object-side focal point of the lens31 to an image-side focal point of the lens 31. The x-axis and they-axis are orthogonal to each other, and also orthogonal to the z-axis.The −x direction is, for example, the gravity direction. For example, inthe example shown in FIG. 3, the +x direction, the +y direction, and +zdirection are a direction from the lower side to the upper side, adirection from the back side to the front side that is perpendicular tothe plane of this paper, and a direction from left to right,respectively.

The lens 31 converges a light ray emitted from an object point on asubject at an image point on an imaging plane 61 of the image sensor 60.The lens 31 includes a pair (set) of an object-side lens and animage-side lens. The object-side lens and the image-side lens have thesame optical axis. The object-side lens and the image-side lens aresymmetrical to each other with respect to a surface orthogonal to theoptical axis.

An image-side focal length of the lens 31 is a distance f. A distancebetween the image-side principal point of the lens 31 and the imagingplane 61 is a distance L. The lens 31 is made of, for example, opticalglass; however, the configuration is not limited thereto. The lens 31may be made of, for example, optical plastic such as an acrylic resin(polymethyl methacrylate: PMMA) or polycarbonate (PC). The lens 31 is anexample of a light convergence element.

FIG. 3 shows a case where the lens 31 is a pair of lenses; however, theconfiguration is not limited thereto. The lens 31 may be one lens(single lens) or a lens obtained by combining a plurality of singlelenses (compound lens). The compound lens may be a bonded type or aseparate type.

The first optical filter 33 and the second optical filter 35 restrict asolid angle, of which a zenith direction is +z-axis direction, relativeto light rays passing through the lens 31. The first optical filter 33is arranged at the image-side focal point of the lens 31, as shown inFIG. 3. In other words, the first optical filter 33 is arranged awayfrom the image-side principal point of the lens 31 toward the +z side bythe distance f. The second optical filter 35 is arranged between theobject-side lens and the image-side lens of the lens 31, as shown inFIG. 3. In this configuration, the center of the second optical filter35 and the center of the lens 31 can be made to coincide with each otherin the z-axis direction.

Herein, the configurations of the first optical filter 33 and the secondoptical filter 35 will be described in detail with reference to thedrawings. FIG. 4A is a schematic view showing an example of an x-y crosssection of an aperture of the first optical filter 33 of FIGS. 2 and 3.FIG. 4B is a schematic view showing an example of an x-y cross sectionof an aperture of the second optical filter 35 of FIGS. 2 and 3.

Each of the first optical filter 33 and the second optical filter 35includes a support member (not shown) and a wavelength selecting member.The support member has an aperture. The wavelength selecting member isprovided in the aperture of the support member. Each of the outer shapesof the apertures and the wavelength selecting members of the firstoptical filter 33 and the second optical filter 35 is round, forexample. The centers of the apertures and the wavelength selectingmembers of the first optical filter 33 and the second optical filter 35are located on the z-axis (optical axis OA). The aperture and thewavelength selecting member of the first optical filter 33 are locatedon the image-side focal plane of the lens 31. On the other hand, theaperture and the wavelength selecting member of the second opticalfilter 35 are located on the image-side principal point plane of thelens 31. Each wavelength selecting member has a property of transmittinga light ray of a specific wavelength spectrum. Transmission may beexpressed as passing. Each wavelength selecting member is, for example,a color filter.

Each of the wavelength selecting members of the first optical filter 33and the second optical filter 35 includes a plurality of wavelengthselecting regions. The present embodiment describes, as an example, acase in which a plurality of wavelength selecting regions are provided,for example, coaxially and concentrically, as shown in FIGS. 4A and 4B.Each of the plurality of wavelength selecting regions is provided with ablue color transmitting filter that transmits a blue light ray and a redcolor transmitting filter that transmits a red light ray. The regionsprovided with the blue color transmitting filter and the red colortransmitting filter are the dot-hatched and grid-hatched regions,respectively, in FIGS. 3, 4A, and 4B. In this case, the peak wavelengthof a wavelength spectrum of a blue light ray is 450 nm, for example. Thepeak wavelength of a wavelength spectrum of a red light ray is 650 nm,for example.

Specifically, the wavelength selecting member of the first opticalfilter 33 is divided into a peripheral region All (first peripheralregion) of the focal plane and a central region Alt (first centralregion) of the focal plane, as shown in FIG. 4A. The peripheral regionA11 of the focal plane and the central region A12 of the focal plane area region from a circle having a radius r11 to a circle having a radiusr10 and a region having a radius less than r11, respectively. Thecentral region A12 of the focal plane is located on the optical axis OAof the lens 31. The peripheral region A11 of the focal plane and thecentral region A12 of the focal plane are respectively provided with ablue color transmitting filter and a red color transmitting filter. Theradius r11 is an example of a first distance.

The wavelength selecting member of the second optical filter 35 isdivided into a peripheral region A21 (second peripheral region) on thelens side and a central region A22 (second central region) on the lensside, as shown in FIG. 4B. The peripheral region A21 on the lens sideand the central region A22 on the lens side are a region from a circlehaving a radius r21 to a circle having a radius r20 and a region havinga radius less than r21, respectively. The central region A22 on the lensside is located on the optical axis OA of the lens 31. The peripheralregion A21 on the lens side and the central region A22 on the lens sideare respectively provided with a red color transmitting filter and ablue color transmitting filter. The radius r21 is an example of a seconddistance.

In this manner, the blue color transmitting filter and the red colortransmitting filter are integrally formed in each of the first opticalfilter 33 and the second optical filter 35 according to the presentembodiment. The blue color transmitting filter and the red colortransmitting filter are respectively arranged rotation-symmetricallywith respect to the optical axis OA of the lens 31.

Each of the wavelength selecting members of the first optical filter 33and the second optical filter 35 may further include a transparentmember that transmits a light ray of any wavelength in the visible lightrange and a black member that does not transmit a light ray of anywavelength in the visible light range. The transparent member may beexpressed as a member that transmits white light (visible light).

For the apertures and the wavelength selecting members of the firstoptical filter 33 and the second optical filter 35, the outer shapes andthe shapes of the wavelength selecting regions are not limited to around shape and a concentric shape, but may be in some other shape. Theymay be in an unsymmetrical shape with respect to the optical axis OA. Inother words, the second distance is not necessarily constant around theoptical axis OA.

If the lens 31 is not a pair of lenses, for example, if the lens 31 isone lens, the second optical filter 35 has only to be arrangedadjacently to the lens 31. In this case, the second optical filter 35may be arranged on the +z side or the −z side of the lens 31.

The image sensor 60 is configured to output a light reception intensityof each pixel for a light ray entering the imaging plane 61. In otherwords, the image sensor 60 is configured to output a light receptionposition and a light reception intensity of the light ray entering theimaging plane 61. The image sensor 60 is a charge-coupled device (CCD),for example. The image sensor 60 is a single-plate type color CCD, forexample, but may be a three-plate type color CCD. The image sensor 60 isnot limited to the CCD, and may be an image sensor such as acomplementary metal-oxide semiconductor (CMOS) or another kind of lightreceiving element. The image sensor 60 is arranged on the +z side withrespect to the image-side focal point of the lens 31. The imaging plane61 of the image sensor 60 is arranged away from the image-side principalpoint of the lens 31 toward the z-axis direction by a distance L. Theimaging plane 61 is located on the light convergence plane of the lens31. The imaging axis IA of the image sensor 60 is located off of theoptical axis OA of the lens 31 as indicated by an arrow M in FIG. 3. Theimaging axis of the image sensor 60 is parallel to the optical axis OA(the z-axis) of the lens 31. The image sensor 60 is arranged in a mannerthat the imaging plane 61 is located in an effective region EA. In theexample shown in FIG. 3, the imaging plane 61 of the image sensor 60 islocated away from the optical axis OA by a separation distance d.

The effective region EA according to the present embodiment will bedescribed below with reference to the drawings. FIG. 5A is a schematicview of an x-z cross section for explaining the effective region EA forthe optical device 20 of FIG. 1. FIG. 5B is a schematic view of an x-ycross section for explaining the effective region EA for the opticaldevice 20 of FIG. 1. In FIGS. 5A and 5B, the effective region EA is thehatched region. For viewability, only a part of the effective region EAis shown in FIG. 5A.

The effective region EA does not cross the optical axis OA. In theeffective region EA, preferably, it is possible to image both of a lightray passing through the telecentric optical system 40 and a light raypassing through the non-telecentric optical system 50 of light raysemitted from the same object point O.

As shown in FIGS. 5A and 5B, for example, the effective region EA is aregion that opens in a direction (the +z direction) from the secondoptical filter 35 toward the first optical filter 33 in a regionsurrounded by a first curved surface EB1, a second curved surface EB2,and a third curved surface EB3. Herein, the first curved surface EB1 isa curved surface that passes through the center of the first opticalfilter 33 and the edge portion (outer periphery) of the peripheralregion A21 on the lens side of the second optical filter 35. The secondcurved surface EB2 is a curved surface that passes through the center ofthe first optical filter 33 and the edge portion of the central regionA22 on the lens side. The third curved surface EB3 is a curved surfacethat passes through the edge portion of the central region A12 of thefocal plane and the edge portion of the central region A22 on the lensside.

As in the optical system 30 according to the present embodiment, if thesize of the central region A22 on the lens side is similar to the sizeof the central region A12 of the focal plane by which telecentricity canbe guaranteed, the second curved surface EB2 and the third curvedsurface EB3 may be considered as approximately the same curved surface.In such a case, the effective region EA may be expressed as a regionthat opens in a direction (the +z direction) from the second opticalfilter 35 toward the first optical filter 33 in a region surrounded bythe first curved surface EB1 and the third curved surface EB3, forexample. Accordingly, the imaging plane 61 has only to be provided at aposition away from the optical axis OA by a distance equal to or morethan the radius r11 of the central region A12 of the focal plane of thefirst optical filter 33.

The second curved surface EB2 may also be defined as a curved surfacepassing through a first point on the edge of the central region A12 ofthe focal plane and a second point on the edge of the central region A22on the lens side, and the first and second points may be defined assymmetrical to each other with respect to the optical axis OA.

If the edge portion of the lens 31 is closer to the optical axis OA thanthe edge portion of the peripheral region A21 on the lens side, thefirst curved surface EB1 is a curved surface that passes through thecenter of the first optical filter 33 and the periphery of the lens 31.

Processing circuitry 70 is an integrated circuit such as a centralprocessing unit (CPU) or an application specific integrated circuit(ASIC). A general purpose computer may be used as the processingcircuitry 70. The processing circuitry 70 is not limited to beingprovided as a dedicated circuit, and may be provided as a program to beexecuted in a computer. In this case, the program is recorded in amemory area in the integrated circuit, the memory 80, etc. Theprocessing circuitry 70 is coupled to the image sensor 60 and the memory80. The processing circuitry 70 calculates information pertaining to thesubject based on the output from the image sensor 60. The processingcircuitry 70 implements an acquisition function 71 and a calculationfunction 72.

In the acquisition function 71, the processing circuitry 70 acquires theintensity for each of R, G, and B in a light beam entering each pixel ofthe imaging plane 61 based on the output from the image sensor 60. Inother words, the processing circuitry 70 performs color separation forimage data output from the image sensor 60, thereby generating imagedata for respective colors.

In the calculation function 72, the processing circuitry 70 calculatesinformation pertaining to the subject based on the image data forrespective colors. Specifically, the processing circuitry 70 specifies,from image data of a plurality of colors, an image (imaging position) ofa given object point on the subject produced by the light ray emittedfrom the object point. The processing circuitry 70 calculates thethree-dimensional position of the object point on the subject based onthe specified imaging position. The three-dimensional position of theobject point on the subject is an example of the information pertainingto the subject. Thus, it may also be expressed that the informationpertaining to the subject includes a three-dimensional shape of thesubject.

The processing circuitry 70 may exist outside the optical test apparatus10. In this case, the output from the image sensor 60 may be outputoutside the optical test apparatus 10 or recorded in the memory 80. Inother words, the information pertaining to the subject may be calculatedinside or outside the optical test apparatus 10.

The memory 80 stores the output from the image sensor 60 or theprocessing circuitry 70. The memory 80 stores the focal length f of thelens 31, the distance L between the lens 31 and the imaging plane 61 inthe z direction, the position of the imaging plane 61 with respect tothe optical axis OA of the lens 31, the arrangement of the wavelengthselecting region of the first optical filter 33, and the arrangement ofthe wavelength selecting region of the second optical filter 35. Thememory 80 is a nonvolatile memory such as a flash memory, for example;however, the memory 80 may be a storage device such as a hard disk drive(HDD), a solid state drive (SSD), or an integral circuit storage device,and may further include a volatile memory.

The display 90 displays the output from the processing circuitry 70. Theoutput from the processing circuitry 70 includes, for example, an imageand an operation screen based on the image data output from the imagesensor 60. The display 90 is a liquid crystal display or an organic ELdisplay, for example. The display 90 is not necessarily provided. Inthis case, the output from the processing circuitry 70 may be recordedin the memory 80, displayed on a display provided outside the opticaltest system 1, or recorded in a memory provided outside the optical testsystem 1.

Next, the operation of the optical test system 1 according to thepresent embodiment will be described in detail with reference to thedrawings. In the optical test system 1, measurement processing andcalculation processing are performed.

[Measurement Processing]

FIG. 6 is a schematic view for explaining an example of a ray path inthe optical device 20 of FIG. 1. As shown in FIG. 6, light raysincluding light rays B and R are emitted from a given object point O onthe subject surface. These light rays are light rays of environmentlight or the like reflected or scattered at the object point O. Assumethat the environment light is white light. As shown in FIG. 6, among thelight rays emitted from the given object point O, light rays passingthrough the first optical filter 33 and the second optical filter 35enter the imaging plane 61 of the image sensor 60 by the lens 31. In themeasurement processing, the image sensor 60 performs imaging for thelight rays entering the imaging plane 61.

First, consider light rays that have a principal ray parallel to theoptical axis OA of the lens 31 when the light rays enter the lens 31.Among these light rays, a light ray R passing through the peripheralregion A21 on the lens side of the second optical filter 35 is a redlight ray. In addition, a light ray B passing through the central regionA22 on the lens side is a blue light ray. These light rays enter thecentral region A12 of the focal plane of the first optical filter 33arranged at the image-side focal point of the lens 31. The blue lightray B among the light lays entering the central region A12 of the focalplane does not have a red wavelength component; thus, the blue light rayB cannot be transmitted through the central region A12 of the focalplane. On the other hand, the red light ray R can be transmitted throughthe central region A12 of the focal plane.

Accordingly, the optical system 30 is a telecentric optical system 40that has telecentricity on the object side for the red light ray R. Inother words, the telecentric optical system 40 is an object-side(subject side) telecentric optical system that passes a red light ray.In the object-side telecentric optical system, an entrance pupil islocated at an infinite position, and the optical axis OA and a principalray are parallel to each other in an object space. Herein, thetelecentric optical system 40 includes the lens 31, the first opticalfilter 33, and the second optical filter 35. The telecentric opticalsystem 40 is an example of the first optical system.

Next, consider light rays that have a principal ray not parallel to theoptical axis OA of the lens 31 when the light rays enter the lens 31.These light rays do not enter the central region A12 of the focal plane.In other words, these light rays enter the peripheral region A11 of thefocal plane, or are directed to a region outside the peripheral regionA11 of the focal plane. The light rays directed to a region outside theperipheral region A11 of the focal plane are not imaged in the opticaldevice 20 according to the present embodiment. The red light ray R amongthe light rays entering the peripheral region All of the focal planedoes not have a blue wavelength component; thus, the light ray R cannotbe transmitted through the central region A11 of the focal plane. On theother hand, the blue light ray B can be transmitted through theperipheral region A11 of the focal plane.

Accordingly, the optical system 30 may be expressed as a non-telecentricoptical system 50 having no telecentricity on the object side relativeto the blue light ray B. In other words, the non-telecentric opticalsystem 50 is a normal lens optical system that passes a blue light ray.The normal lens optical system includes an optical system that does nothave telecentricity such as an entocentric optical system, amagnification optical system, or a reduction optical system. Thenon-telecentric optical system 50 includes the lens 31, the firstoptical filter 33, and the second optical filter 35. The non-telecentricoptical system 50 is an example of the second optical system.

As described above, the optical system 30 according to the presentembodiment includes a telecentric optical system 40 and anon-telecentric optical system 50. The optical axis of the telecentricoptical system 40 coincides with the optical axis of the non-telecentricoptical system 50. Furthermore, the telecentric optical system 40 sharesat least one lens with the non-telecentric optical system 50. The sharedlens is the lens 31, for example.

The red light ray R transmitted through the central region A12 of thefocal plane and the blue light ray B transmitted through the peripheralregion A11 of the focal plane enter the imaging plane 61. As describedabove, in the measurement processing, the image sensor 60 simultaneouslyreceives the red light ray R passing through the optical system 30 asthe telecentric optical system and the blue light ray B passing throughthe optical system 30 as the non-telecentric optical system among thelight rays emitted from a given object point O. The image sensor 60converts the light ray R and the light ray B into electric signals andA/D-converts the electric signals, thereby generating image data for thesubject. The image sensor 60 outputs the image data to the processingcircuitry 70. The image data indicates the space distribution of thesubject. The image data illustrates an image produced by the light ray Rand an image produced by the light ray B for each object point on thesubject. Herein, the position of the image produced by the light ray Rpassing through the telecentric optical system 40 does not change inaccordance with the distance from the object point to the image sensor60. On the other hand, the position of the image produced by the lightray B passing through the non-telecentric optical system 50 changes inaccordance with the distance from the object point to the image sensor60. Accordingly, a distance between an image produced by the light ray Rand an image produced by the light ray B relative to the same objectpoint changes in accordance with the distance from the object point tothe image sensor 60. A distance from the image sensor 60 to the objectpoint or to the subject is obtained by measuring or observing thedistance between an image produced by the light ray R and an imageproduced by the light ray B in the image data. The image produced by thelight ray R and the image produced by the light ray B are examples of afirst image and a second image, respectively.

[Calculation Processing]

FIG. 7 is a flowchart showing an example of the calculation processingperformed by the optical test apparatus 10 of FIG. 1 In the calculationprocessing, the processing circuitry 70 calculates the three-dimensionalshape of the subject based on the output from the image sensor 60.

The processing shown in FIG. 7 is started after acquiring the image dataobtained by imaging in the measurement processing.

In step S11, the processing circuitry 70 performs color extractionprocessing. In the color extraction processing, the processing circuitry70 performs color separation for the acquired data, thereby extractingimage data for respective colors. Although the image data is described,the data is not limited to data that can be displayed as an image, andit is only necessary to extract a light ray intensity for each pixel ofeach color of the image sensor 60.

In step S12, the processing circuitry 70 performs the image planeposition acquisition processing. The processing circuitry 70 specifiesthe imaging positions for respective colors based on the image data forrespective colors. The imaging positions can be expressed as theincident positions of the light rays on the imaging plane 61. Theprocessing circuitry 70, for example, performs image processing such asedge enhancement for the image data, and specifies an imaging positioncorresponding to the object point O. At this time, image processing suchas pixel matching may be performed for the shape of the detected edge,for example.

A point light source may be used as the object point O. In this case,for example, a position with high luminance in the image data may bespecified as an imaging position. A transmissive dot pattern, forexample, may be used as the object point O. In this case, for example,the above-described image processing such as edge detection or pixelmatching may be performed.

In step S13, the processing circuitry 70 performs the object pointposition calculation processing. In the object point positioncalculation processing, the processing circuitry 70 calculates thethree-dimensional position of the object point O of the subject based onthe imaging positions of the light rays for the respective colors on theimaging plane 61.

The object point position calculation processing will be described indetail below.

(x, y, z) represent coordinates indicating the position of the objectpoint O in three-dimensional space. As shown in FIG. 6, (p, q) representcoordinates indicating the incident position of the red light ray R onthe imaging plane 61, the red light ray R emitted from the object pointO and passing through the optical system 30 as a telecentric opticalsystem. In addition, (P, Q) represent coordinates indicating theincident position of the blue light ray B on the imaging plane 61, theblue light ray B emitted from the object point O and passing through theoptical system 30 as a non-telecentric optical system. Herein, theorigin of the coordinates indicating the incident positions of the lightrays on the imaging plane 61 is on the optical axis OA. The processingcircuitry 70 acquires, from the memory 80, for example, the position ofthe imaging plane 61 with respect to the optical axis OA of the lens 31.The processing circuitry 70 acquires, from the image sensor 60, anincident position of each light ray in the coordinate system on theimaging plane 61. The processing circuitry 70 calculates coordinatesindicating an incident position of each light ray on the imaging plane61 by using the position of the imaging plane 61 with respect to theoptical axis OA of the lens 31 and an incident position of each lightray in the coordinate system on the imaging plane 61.

At this time, by geometric optics, the imaging position of the bluelight ray B passing through the optical system 30 as a non-telecentricoptical system is expressed by the following equation:

$\begin{matrix}{\begin{bmatrix}P \\Q\end{bmatrix} = {{\left( \frac{L}{z} \right)\begin{bmatrix}x \\y\end{bmatrix}} \pm {{\left( {{\frac{L}{f}\left( {1 - \frac{f}{z}} \right)} - 1} \right)\begin{bmatrix}r_{0} \\r_{0}\end{bmatrix}}.}}} & {{Eq}.\mspace{14mu} (1)}\end{matrix}$

The second term on the right side of Equation (1) represents a marginalray passing through the end portion of the central region A22 on thelens side of the second optical filter 35.

On the other hand, by geometric optics, the imaging position of the redlight ray R passing through the optical system 30 as a telecentricoptical system is expressed by the following equation:

$\begin{matrix}{\begin{bmatrix}p \\q\end{bmatrix} = {{\left( {\frac{L}{f} - 1} \right)\begin{bmatrix}x \\y\end{bmatrix}} \pm {{\left( {\frac{L}{f} - {\frac{1}{f}\left( {\frac{L}{f} - 1} \right)z}} \right)\begin{bmatrix}r_{1} \\r_{1}\end{bmatrix}}.}}} & {{Eq}.\mspace{14mu} (2)}\end{matrix}$

The second term on the right side of Equation (2) represents a marginalray passing through the end portion of the central region A12 of thefocal plane of the first optical filter 33.

Based on Equations (1) and (2), the position of the object point O inthe three-dimensional space is expressed by the following equation byusing the imaging position of each light ray:

$\begin{matrix}{\begin{bmatrix}x \\y \\z\end{bmatrix} = {\begin{bmatrix}{\frac{f}{L - f}p} \\{\frac{f}{L - f}q} \\\frac{{Lf}\sqrt{p^{2} + q^{2}}}{L - {f\sqrt{P^{2} + Q^{2}}}}\end{bmatrix}.}} & {{Eq}.\mspace{14mu} (3)}\end{matrix}$

The processing circuitry 70 calculates the three-dimensional position ofthe object point O based on the imaging data using equation (3). In theimage plane position acquisition processing, the plurality of imagingpositions corresponding to a plurality of object points O on the subjectare acquired for each color; thus, a three-dimensional shape of thesubject can be calculated based on the imaging data. Informationpertaining to the subject, such as the calculated three-dimensionalshape of the subject, is displayed on the display 90.

As described above, the optical test system 1 according to the presentembodiment can effectively use the region on the imaging plane, whichleads to measurement of the three-dimensional position of the objectpoint O with a high degree of accuracy. The three-dimensional positionof the object point O is an example of the information pertaining to thesubject. In other words, with the technique according to the presentembodiment, the three-dimensional surface shape of the subject can bemeasured with a high degree of accuracy. The technique of contactlessmeasurement of a distance to an object and a three-dimensional shape ofan object may be applied to various uses. For example, there is a demandfor a technique of measuring a distance to an object in the fieldrelated to a car-mounted camera and machine vision. For example, thereis a demand for a technique of measuring a three-dimensional surfaceshape in the field related to product inspection in manufacturing andnon-destructive inspection of infrastructure. Under such circumstances,according to the present technique, at minimum, one image sensor 60suffices. Furthermore, according to the present technique, measurementcan be performed by using the environmental light scattered on anobject. Therefore, measurement can be performed without preparing twoimage sensors as in a stereo camera or preparing a light source (aprojector) as in a structured illumination. In other words, according tothe present technique, an effect of cost reduction and size reductioncan be obtained.

In the optical test system 1 according to the present embodiment, theimaging plane 61 of the image sensor 60 is arranged in the effectiveregion EA. The imaging axis IA of the image sensor 60 is arranged awayfrom the optical axis OA of the optical system 30. Such configurationhas the following effects.

FIG. 8 is a diagram for explaining the relationship between a distancebetween the optical axis OA and the imaging axis IA in the opticaldevice 20 of FIG. 1, and detection sensitivity for a three-dimensionalposition of an object point O. FIG. 8 shows a numerical analysis resultfor the relationships between the optical axis OA located away from thelens 31 by the distance L and light ray positions in the optical device20 of FIG. 1. FIG. 8 may be expressed as a numerical analysis result forlight received by the image sensor 60′ of FIG. 3. In FIG. 8, points 1 to22 respectively indicate different object points O on the subject. Thepositions of points 1 to 11 in the z direction are the same as positionsof the points 12 to 22 in the z direction, respectively. The objectpoint O is located in the +z direction in the order of 1 to 11 or 12 to22. In FIG. 8, the dot hatching and the grid hatching respectivelyindicate light ray positions of the blue light ray B and light raypositions of the red light ray R.

Generally, a lens is designed to produce the highest performance on theoptical axis. Thus, if the imaging axis is brought away from the opticalaxis, measurement accuracy may decrease. On the other hand, as shown inFIG. 8, in the optical device 20 according to the present embodiment,the intervals between the imaging positions relative to the points 12 to22 are larger than the intervals between the imaging positions relativeto the points 1 to 11, respectively. In other words, according to thenumerical analysis result shown in FIG. 8, the position gap between redand blue becomes larger at a position further away from the optical axisOA even if the subject is at the same distance. Herein, as describedabove, a three-dimensional position of an object point O is calculatedbased on difference between the imaging position of a blue light ray Band the imaging position of a red light ray R. Accordingly, in a regionwith a larger position gap between red and blue in FIG. 8, an imagemoves more sensitively in response to a fine movement of an object inthe z direction. In other words, the further the imaging axis IA is awayfrom the optical axis OA, the higher the detection sensitivity becomes.In the optical test system 1 according to the present embodiment, theimaging axis IA of the image sensor 60 is located away from the opticalaxis OA of the optical system 30, which enables imaging of a region faraway from the optical axis. In other words, an effect of improving thedistance detection sensitivity is obtained by the present technique.

FIG. 9 is a diagram for explaining an unmeasurable region in the opticaldevice 20 of FIG. 1. FIG. 9 shows a measurement result indicating theoptical axis OA located away from the lens 31 by the distance L and alight ray position of the light ray R relative to light rays emittedfrom the subject having a checker pattern in the optical device 20 ofFIG. 1. FIG. 9 may be expressed as a measurement result for lightreceived by the image sensor 60′ of FIG. 3. In FIG. 9, the grid hatchingindicates a light ray position of the red light ray R. As explained withreference to FIG. 6, a red wavelength component of the light raysemitted from the subject cannot be transmitted through the centralregion A22 on the lens side. The red light ray R that can be transmittedthrough the peripheral region A21 on the lens side can be transmittedthrough the central region A12 of the focal plane (the image-side focalpoint of the lens 31), but cannot be transmitted through the peripheralregion A11 of the focal plane. Accordingly, as shown in FIG. 9, thelight ray R emitted from the object point O of the subject on theoptical axis OA cannot be imaged on the optical axis OA. A light emittedfrom the object point O on the optical axis OA may reach the imagingplane 61 depending on, for example, performance and characteristicsrelating to wavelength selectivity of the optical filter. However, theobject point O on the optical axis OA is represented by (p, q)=(P,Q)=(0, 0); thus, as understood from Equation (3), a three-dimensionalposition of the object point O on the optical axis OA cannot becalculated, regardless of performance and characteristics relating towavelength selectivity of the optical filter. Under such circumstances,in the optical test system 1 according to the present embodiment, theimaging axis IA of the image sensor 60 is located away from the opticalaxis OA of the optical system 30, and the optical axis OA can beexcluded from the imaging range of the image sensor 60. In other words,according to the present technique, a distance to the subject can becalculated by imaging the subject by using all the pixels of the imagesensor 60. An increase in the number of pixels which can be used forimaging contributes to improvement in accuracy of detecting an imagingposition on the imaging plane 61.

FIG. 10 is a diagram for explaining a measurable region in the opticaldevice 20 of FIG. 1. As shown in FIG. 10, distribution of the measurableregion in a case where the imaging axis IA coincides with the opticalaxis OA is different from distribution of the measurable region in acase where the imaging axis IA is arranged away from the optical axisOA. Since the subject on the optical axis OA cannot be imaged asdescribed above, the measurable region is cylindrical if the imagingaxis IA is made to coincide with the optical axis OA. In other words, ifa subject is at the position including the optical axis OA (for example,the photographic subject P of FIG. 10), the entire subject cannot bemeasured. On the other hand, if the imaging axis IA is arranged awayfrom the optical axis OA, the measurable region can be columnar. Inother words, the present technique has an effect that a measurableregion focusing on the observed subject can be formed.

FIRST MODIFICATION

An optical test system 1 according to the present modification will bedescribed in detail below with reference to the drawings. Differencesfrom the first embodiment will mainly be described. The same referencenumerals denote the same parts, and a description thereof will beomitted.

The first embodiment describes, as an example, the case where the sizeof the central region A22 on the lens side is similar to the size of thecentral region A12 of the focal plane by which telecentricity can beguaranteed. However, the configuration is not limited thereto. Thepresent technique can increase the size of the central region A22 on thelens side.

FIG. 11 is an x-z cross-sectional view showing an example of theconfiguration of an optical device 20 according to the presentmodification. As described above with reference to FIGS. 5A, 5B, and 10,etc., by the present technique, instead of reducing the diameter of thecentral region A22 on the lens side of the second optical filter, asubject near the optical axis OA can be photographed by separating theimaging axis IA from the optical axis OA. In other words, as shown inFIG. 11, the central region A22 on the lens side may be made larger thanthe central region A12 of the focal plane by separating the imaging axisIA from the optical axis OA.

Expansion of the central region A22 on the lens side contributes toincrease in light amount of a blue light ray B that can be transmittedthrough the central region A22 on the lens side. Thus, a brighter imagecan be obtained. In addition, image forming capability relative to ablue light ray B can be improved. Therefore, according to theconfiguration of the present modification, the measurement accuracy canbe further improved.

SECOND MODIFICATION

An optical test system 1 according to the present modification will bedescribed in detail below with reference to the drawings. Differencesfrom the first embodiment will mainly be described. The same referencenumerals denote the same parts, and a description thereof will beomitted.

The first embodiment describes, as an example, the optical system 30having telecentricity and non-telecentricity in accordance withwavelength components of the light rays emitted from the object point Oon the subject. However, the configuration is not limited thereto. Eachof the first optical filter 33 and the second optical filter 35 has onlyto have a characteristic selecting region that selectively transmitslight in accordance with characteristics of the light. For example, thepresent technique can realize an optical system 30 having telecentricityand non-telecentricity in accordance with polarization components oflight rays emitted from the object point O on the subject.

Unlike in the first embodiment, the image sensor 60 according to thepresent modification is a polarization camera configured to image atleast two polarized regions. The polarization camera is, for example,the image sensor 60 according to the first embodiment further includinga polarization plate (a polarizer, a polarizing filter). Thepolarization plate is provided on the imaging plane 61. The image sensor60 outputs, to the processing circuitry 70, image data including lightray positions of respective polarization components.

The processing circuitry 70 according to the present modificationdivides the image data according to the respective polarizationcomponents in step S11 in FIG. 7. After that, the processing circuitry70 specifies imaging positions of respective polarization components(step S12), and calculates information pertaining to the subject basedon the specified imaging positions (step S13).

FIG. 12A is a schematic view showing an example of an x-y cross sectionof an aperture of the first optical filter 33 according to the presentmodification. FIG. 12B is a schematic view showing an example of an x-ycross section of an aperture of the second optical filter 35 accordingto the present modification. As shown in FIGS. 12A and 12B, theperipheral region A11 of the focal plane of the first optical filter 33and the central region A22 on the lens side of the second optical filter35 according to the present modification transmit light rays having thesame polarization direction. The central region A12 of the focal planeand the peripheral region A21 on the lens side transmit light rayshaving the same polarization direction. Meanwhile, the central regionA12 of the focal plane and the peripheral region A21 on the lens sidetransmit light rays having a different polarization direction from theperipheral region A11 of the focal plane and the central region A22 onthe lens side. The region that selectively transmits light in accordancewith polarization of light at the first optical filter 33 and the secondoptical filter 35 according to the present modification is an example ofa polarization selecting region.

Even in such configuration, the optical system 30 may havenon-telecentricity for a light ray having a polarization directionparallel to the x-axis, and have telecentricity on the object side for alight ray having a polarization direction orthogonal to the x-axis.Furthermore, according to the technique of the present modification, thethree-dimensional position with respect to the object point O on thesubject and the three-dimensional shape of the surface of the subjectcan be calculated regardless of wavelength characteristics of thesubject.

The technique according to the present modification can be combined withthe technique according to the first modification. In other words, evenin the case of using the difference in polarization direction, theamount of light passing through the non-telecentric optical system 50can be increased.

The technique according to the present modification can be combined withthe technique according to the first embodiment. For example, each ofthe wavelength selecting members of the first optical filter 33 and thesecond optical filter 35 may have a plurality of wavelength selectingfilters and a plurality of polarization filters. In this case, theplurality of wavelength selecting filters and the plurality ofpolarization filters may be arranged in series with respect to alightray passing therethough, or may be arranged in different regions in eachoptical filter. For example, a wavelength selecting filter and apolarization selecting filter may be configured to be replaceable witheach other. For example, the optical filters may be configured to beswitchable with each other. For example, the optical test apparatus 10may be provided with an optical system using a wavelength selectingfilter and an optical system using a polarization selecting filter, andthe optical systems may be switched in accordance with a measurementtarget. With such configurations, information pertaining to the subjectcan be calculated if either one of a wavelength and a polarizationdirection is measurable. In other words, types of a measurable subjectcan be increased. The accuracy of calculation of information pertainingto the subject can be improved if both of a wavelength and apolarization direction are measurable.

The above embodiment and modifications describe, as an example, the caseusing one image sensor 60; however, the configuration is not limitedthereto. According to the present technique, since the imaging axis IAis provided away from the optical axis OA, a plurality of imaging axesIA can be set around the optical axis OA. In other words, a plurality ofimage sensors 60 may be provided in the effective region EA. In thiscase, the plurality of image sensors 60 are examples of a first imagesensor and a second image sensor. FIG. 13 is a schematic view of the x-ycross section for explaining an example of an arrangement of the imagingplanes 61 in a case where the optical device 20 of FIG. 1 has aplurality of image sensors 60. As shown in FIG. 13, each of theplurality of imaging axes IA of the plurality of image sensors 60 isarranged at a position off of the optical axis OA. The plurality ofimaging planes 61 of the plurality of image sensors 60 are provided inthe effective region EA. In the example shown in FIG. 13, the pluralityof imaging planes 61 are arranged in a circle. The number of theplurality of image sensors 60 may be two to seven, or a plural numberequal to or more than nine. The plurality of image sensors 60 mayinclude, for example, at least one color CCD and at least onepolarization camera. In this case, it is only necessary that the type ofan optical filter corresponds to the type of an image sensor in eachpair, and the arrangement and number of the color CCDs and polarizationcameras may be set discretionarily. The arrangement of the plurality ofimage sensors 60 is not limited to a circle, and the distances from theoptical axis to the respective image sensors 60 may be different fromeach other.

The above embodiment and modifications describe, as an example, the casewhere each optical filter is divided into two regions. However, theconfiguration is not limited thereto. Each optical filter may be dividedinto three or more regions. The number into which the first opticalfilter 33 is divided may be different from the number into which thesecond optical filter 35 is divided.

In the configuration of FIG. 3, for example, the edge portion(periphery) of the second optical filter 35 may be further provided witha region that does not transmit a red wavelength component such as aregion that transmits blue light rays and a region that does nottransmit visible light rays. According to this configuration, it ispossible to eliminate red light rays transmitted through the end portionof the lens 31 that has lower performance than on the optical axis, andlight rays scattered at the end portions of the lens 31 and the secondoptical filter 35, etc. In other words, this configuration has theeffect of reducing noise.

The above embodiment and modifications describe, as an example, a casewhere information pertaining to the subject including the object point Ois calculated based on environment light scattered at the object pointO. However, the configuration is not limited thereto. For example, theoptical test apparatus 10 may further include a light source such as alight-emitting diode (LED), and a target for measurement such as a dotpattern and a checker pattern. In this case, a position and a shaperelative to the target for measurement are calculated as informationpertaining to the subject. The characteristics of each optical filtercan be optimized if the measurement target is known, which leads tofurther improvement of the measurement accuracy.

The above embodiment and modifications describe, as an example, a casewhere information pertaining to the subject is calculated based on adifference in imaging position between a plurality of wavelengths and adifference in imaging position between a plurality of polarizations.However, the configuration is not limited thereto. For example, bymeasuring time-series variation of the imaging position,presence/absence of refractive-index distribution in thethree-dimensional space (the −z side of the lens 31) may be calculatedas information pertaining to the subject. The second optical filter 35is not necessarily provided.

The above embodiment and modifications describe, as an example, a casewhere the telecentric optical system 40 and the non-telecentric opticalsystem 50 have the same optical axis. However, the configuration is notlimited thereto. It is only necessary to measure two light raysrespectively passing through the telecentric optical system 40 and thenon-telecentric optical system 50, among the light rays emitted from theobject point O, on an imaging plane having an imaging axis differentfrom an optical axis of the telecentric optical system 40 and an opticalaxis of the non-telecentric optical system 50. With this configuration,measurement can be performed not only between the optical system 30 andthe image sensor 60, which leads to improvement of design flexibility.Furthermore, with this configuration, the subject on the optical axiscan be imaged.

In the above embodiment and modifications, the telecentric opticalsystem 40 and the non-telecentric optical system 50 may respectivelyhave telecentricity on the image side. In this case, the configurationof FIG. 3, for example, further includes a lens arranged on the opticalaxis OA in a manner that the first optical filter 33 is located at theobject-side focal point. Herein, for example, the effective region EA isa region obtained by excluding, from a region which is on the image sideof the further-arranged lens and is equal to or less than a lengthobtained by multiplying the radius from the optical axis OA to the edgeportion of the peripheral region A21 on the lens side by themagnification ratio of the optical system 30, a region less than alength obtained by multiplying the radius from the optical axis OA tothe edge portion of the central region A22 on the lens side by themagnification ratio of the optical system 30.

In the above explanation, the image sensor 60 is assumed to be arrangedin the effective region EA. However, the present embodiment and themodifications do not hinder the image sensor 60 from being arranged in aregion other than the effective region EA. For example, the opticaldevice 20 may include an image sensor 60 arranged in the effectiveregion EA and an image sensor 60 arranged in a region other than theeffective region EA. In this case, driving of the image sensor 60arranged in a region other than the effective region EA is preferablystopped at the time of imaging. As a result, the distance can bemeasured similarly to a case where the image sensor 60 is arranged onlyin the effective region EA. Furthermore, the image sensor 60 arranged inthe effective region EA and the image sensor 60 arranged in a regionother than the effective region EA may be driven at the time of imaging.In this case, the processing circuitry 70 may measure the distance byusing image data from the image sensor 60 arranged in the effectiveregion EA, without using image data from the image sensor 60 arranged ina region other than the effective region EA.

In the above explanation, the wavelength selecting filter and thepolarization selecting filter are described as examples of acharacteristic selecting member provided in the optical filter. However,the configuration is not limited thereto. It is only necessary todetermine whether the image position relative to the light received atthe image sensor 60 is produced by the light passing through thetelecentric optical system 40 or the non-telecentric optical system 50.In other words, the characteristic selecting member may be an intensityfilter, a spatial frequency filter, etc. which selectively transmitlight in accordance with the light intensity and the spatial frequency.As a characteristic selecting member, a liquid crystal filter of whichlight transmission amount varies upon application of a voltage may beused. In this case, relative to the first optical filter 33, forexample, the central region A12 of the focal plane and the peripheralregion A11 of the focal plane are controlled in synchronization with theimaging timing at the image sensor 60 so as to have differenttransmission rates.

The techniques according to the respective embodiments and themodifications can measure information concerning the subject (testobject) with high accuracy.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions, and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. An optical test apparatus comprising: a lightconvergence element for converging light from a subject; an opticalfilter arranged on an optical axis of the light convergence element; andan image sensor that is arranged in an effective region not crossing theoptical axis of the light convergence element, and that receives lightpassing through the light convergence element and the optical filter. 2.The optical test apparatus of claim 1, wherein the optical filterincludes: a first optical filter arranged on an image-side focal planeof the light convergence element; and a second optical filter arrangedon an image-side principal point plane of the light convergence element.3. The optical test apparatus of claim 2, wherein the light convergenceelement includes a pair of lenses symmetrical to each other with respectto a surface orthogonal to the optical axis, and the second opticalfilter is arranged between the pair of lenses.
 4. The optical testapparatus of claim 1, wherein the optical filter includes acharacteristic selecting region that selectively transmits light inaccordance with a characteristic of light.
 5. The optical test apparatusof claim 4, wherein the characteristic selecting region includes awavelength selecting region that selectively transmits light inaccordance with a wavelength and/or a polarization selecting region thatselectively transmits light in accordance with polarization.
 6. Theoptical test apparatus of claim 4, wherein the characteristic selectingregion of the first optical filter includes a first central regionwithin less than a first distance from a focal point of the lightconvergence element, the first central region transmitting light havinga first characteristic, and the effective region is a region separatefrom the optical axis by equal to or more than the first distance. 7.The optical test apparatus of claim 4, wherein the characteristicselecting region of the first optical filter includes: a first centralregion that is provided in a region within less than a first distancefrom a focal point of the light convergence element, and that transmitslight having a first characteristic; and a first peripheral region thatis provided in a region away from the focal point by equal to or morethan the first distance, and that transmits light having a secondcharacteristic different from the first characteristic, and thecharacteristic selecting region of the second optical filter includes: asecond central region that is provided in a region within less than asecond distance from a principal point of the light convergence element,and that transmits light having the first characteristic; and a secondperipheral region that is provided in a region away from the principalpoint by equal to or more than the second distance, and that transmitslight having the second characteristic.
 8. The optical test apparatus ofclaim 7, wherein the second distance is longer than the first distance.9. The optical test apparatus of claim 7, wherein the second distance isnot constant around the optical axis.
 10. The optical test apparatus ofclaim 7, wherein the effective region is a region that opens from thefocal point in an optical axis direction different from the secondoptical filter, and that is included in a region surrounded by a firstcurved surface passing through the focal point and an edge of the secondperipheral region and a second curved surface passing through an edge ofthe first central region and an edge of the second central region. 11.The optical test apparatus of claim 7, further comprising processingcircuitry that calculates, based on output from the image sensor, adistance between an image produced by the light having the firstcharacteristic and an image produced by the light having the secondcharacteristic on an imaging plane of the image sensor, and calculates athree-dimensional position of a point on the subject based on thecalculated distance on the imaging plane.
 12. The optical test apparatusof claim 1, wherein the image sensor includes a first image sensor and asecond image sensor arranged at different positions in the effectiveregion.
 13. An optical test apparatus comprising: a first optical systemthat has telecentricity on an object side for light having a firstcharacteristic, and that passes the light having the firstcharacteristic; a second optical system that passes light having asecond characteristic different from the first characteristic; and animage sensor that is arranged in an effective region not crossing anoptical axis of the first optical system and the second optical system,and that receives light passing through the first optical system andlight passing through the second optical system.
 14. An optical testmethod comprising: imaging an object by an optical device including: afirst optical system that has telecentricity on an object side for lighthaving a first characteristic, and that passes the light having thefirst characteristic; a second optical system that passes light having asecond characteristic different from the first characteristic; and animage sensor that is arranged in an effective region not crossing anoptical axis of the first optical system and the second optical system,and that receives light passing through the first optical system andlight passing through the second optical system; and generating, basedon output from the image sensor, image data in which a distance betweena first image produced by light having the first characteristic and asecond image produced by light having the second characteristic from anidentical point on the object changes in accordance with a distance fromthe point to the image sensor.
 15. The optical test method of claim 14,further including: calculating a distance between the first image andthe second image on an imaging plane of the image sensor, based on theoutput from the image sensor; and calculating a three-dimensionalposition of the point based on the calculated distance on the imagingplane.